JP2503453B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air-fuel ratio control device for an internal combustion engine, which controls an internal combustion engine with an air-fuel mixture having an air-fuel ratio leaner than a theoretical air-fuel ratio.

[Conventional technology]

Conventionally, in air-fuel ratio control, in order to improve fuel efficiency of the internal combustion engine, the air-fuel ratio of the air-fuel mixture is made leaner (A / F = 15 to 20) than the theoretical air-fuel ratio (A / F ≈ 14.8) in the low load region. It is known that a lean sensor is provided in the exhaust system to feedback control the air-fuel ratio so that the air-fuel ratio is set and the set air-fuel ratio is maintained. In this control, the idling state of the internal combustion engine is detected by a switch that detects the full closing of the throttle valve, and when the idling state is detected, the air-fuel ratio is adjusted to a lean air-fuel ratio in a normal low load range in order to maintain the stability of the idling speed. It is also known to control near the stoichiometric air-fuel ratio, which is richer than the fuel ratio.

[Problems to be solved by the invention]

However, if the throttle valve is not returned properly or the throttle valve fully closed detection switch fails, it becomes impossible to detect the idling state. as a result,
Despite the idling state, the air-fuel ratio of the air-fuel mixture to the internal combustion engine is controlled to an air-fuel ratio leaner than the stoichiometric air-fuel ratio, and the output torque of the internal combustion engine is reduced due to slight changes in the air-fuel ratio of the air-fuel mixture. It fluctuates considerably and the idling speed becomes unstable.

 The present invention aims to solve this problem.

[Means for solving problems]

In order to achieve the above object, the present invention, as shown in FIG. 1, includes load detecting means for detecting an engine load state based on at least one operating state of an intake pipe pressure, a rotational speed, and an intake air amount of an internal combustion engine. A throttle valve fully closed detecting means for detecting a fully closed state of a throttle valve as an idling state of the internal combustion engine; and a load detecting means for providing an air-fuel ratio leaner than a theoretical air-fuel ratio in a low load state including an idling state. The lean air-fuel ratio setting means for setting the air-fuel ratio in accordance with the load state detected by, the idling air-fuel ratio setting means for setting the air-fuel ratio in the idling state to approximately the theoretical air-fuel ratio, and the throttle valve fully closed detection means When the fully closed state of the throttle valve is not detected, the throttle valve fully closed detection is performed with the air-fuel ratio set by the lean air-fuel ratio setting means. When the fully closed state of the throttle valve is detected by the output means, air-fuel ratio control means for controlling the air-fuel ratio of the internal combustion engine at the air-fuel ratio set by the idling air-fuel ratio setting means, and the throttle valve fully closed detection Abnormality determining means for determining an abnormality in the operation of the means, and a low load state corresponding to the idling state set by the lean air-fuel ratio detecting means when the abnormality determining means determines the abnormality in the throttle valve fully closed detecting means. And an air-fuel ratio changing means for changing the lean air-fuel ratio to approximately the theoretical air-fuel ratio.

[Action]

With the above configuration, when an abnormality such as a failure of the throttle valve fully closed detection means is determined, the lean air-fuel ratio at the time of low load set by the lean air-fuel ratio setting means is changed to a roughly theoretical air-fuel ratio by the air-fuel ratio changing means. Because of the change, even if the internal combustion engine is in the idling state, it is not operated at the lean air-fuel ratio at the time of low load, but is operated at the changed substantially theoretical air-fuel ratio.

〔Example〕

 The present invention will be described below with reference to embodiments shown in the drawings.

FIG. 2 is an overall configuration diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention. In FIG. 1, the surge tank 3 of the intake passage 2 of the internal combustion engine 1 is provided with a pressure sensor 4 for detecting an intake pressure P _m (absolute pressure of intake air) of the intake passage 2 as an engine load, The output is supplied to the A / D converter 101 with a built-in multiplexer of the control circuit 10. A throttle sensor for detecting the opening of the throttle valve 5 is provided on the rotary shaft of the throttle valve 5 provided in the intake passage 2 of the internal combustion engine 1. This throttle sensor has a built-in fully-closed switch 6 which is turned on only when the opening degree θ of the throttle valve 5 becomes equal to or less than θ ₁ (for example, 1.5 °) corresponding to the fully closed state. The off output is supplied to the input / output interface 103 of the control circuit 10. Further, the exhaust passage 7 of the engine 1 is provided with a known lean sensor 8 for detecting the oxygen concentration in the exhaust gas for feedback control of the air-fuel ratio. Since the output of the lean sensor 8 is obtained as a current output according to the oxygen concentration in the exhaust gas, that is, the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 1, it is converted into a voltage by the current-voltage conversion circuit 102 of the control circuit 10. And then supplied to the A / D converter 101.

In order to detect the rotational position and rotational speed of the internal combustion engine 1, the distributor 9 has a crank angle sensor 11 whose axis generates a reference position detection pulse signal every 720 ° converted into a crank angle, for example. Further, a crank angle sensor 12 is provided which generates a pulse signal for detecting an angular position every 30 ° converted into a crank angle. The pulse signals of the crank angle sensors 11 and 12 are supplied to the input / output interface 103 of the control circuit 10.

Further, in the intake passage 2, the drive circuit 104 of the control circuit 10
Each cylinder is provided with a fuel injection valve 13 for supplying the pressurized fuel from the fuel supply system to the intake port, and controls the fuel injection amount to control the air-fuel ratio of the air-fuel mixture.
The vehicle speed sensor 14 detects the traveling speed of a vehicle (not shown) equipped with the internal combustion engine 1, and supplies a pulse to the input / output interface 103 of the control circuit 10 every time the vehicle travels a predetermined distance.

The control circuit 10 is configured as, for example, a microcomputer, and includes the A / D converter 101 and the current-voltage conversion circuit 1 described above.
0, outside interface 103, CPU105, ROM106, RAM107
Is provided. Note that the ROM 106 stores in advance a program for controlling the calculation of the CPU 105 and various data used for this calculation. As this data, the air-fuel ratio characteristics preset and stored in the ROM 106 according to the operating state of the internal combustion engine 1 are illustrated in FIGS. 3 and 4. The RAM 107 temporarily stores the detected values detected by the respective sensors and various calculated values obtained by the calculation of the CPU 105.

Next, the arithmetic processing executed by the CPU 105 of the control circuit 10 will be described together with the overall operation of the present embodiment with reference to the flow charts shown in FIGS.

FIG. 5 is a routine for detecting an abnormality of the fully closed switch 6 for detecting the idle state, which is executed as a part of the main routine or every predetermined time or every predetermined crank angle. First, in step 501, it is determined whether or not the vehicle is in a traveling state (vehicle speed> 0) based on the vehicle speed data obtained by the interface 103 by counting the pulses from the vehicle speed sensor 14. If the vehicle speed = 0 (vehicle stopped), the output of the fully closed switch 6 is determined in step 502. if,
If the output indicates that the fully closed switch 6 is in the off state, the content of a flag S, which will be described later, indicating whether or not the vehicle has just stopped from the traveling state is determined in step 503, and the content indicates the previous vehicle traveling. If "0", a counter CF that measures the number of times the output of the fully closed switch 6 is turned off in step 504
Count up by adding 1 to the previous value of iDL. In step 505, the value of CFiDL is equal to or greater than a predetermined value (for example, 8), that is, when the vehicle is in a stopped state immediately after traveling (in this case, the throttle valve 5 should be fully closed in the idling state and the fully closed switch 6 should be on). When the output of the closing switch 6 is detected to be off eight times or more, it is determined that the fully closing switch 6 is abnormal, and the fully closing switch abnormality determination flag F is set in step 506 to indicate that the fully closing switch 6 is abnormally operated. "I will. Step
At 507, a predetermined value (8) is substituted so that the value of CFiDL does not overflow. In the next step 508, the flag S is set to "1" indicating that the vehicle is stopped, and steps 504 to 507 are bypassed until the flag S becomes "0" again.
That is, steps 504 to 507 are executed only once immediately after the vehicle is stopped from the running state.

If it is determined in step 501 that the vehicle is running, the step 504
To execute steps 507 to 507, the flag S is set to "0" in step 509.

According to the above processing, when the output of the fully closed switch 6 is detected to be off a predetermined number of times (8 times) or more when the vehicle shifts from the traveling state to the stopped state, it is determined that the fully closed switch 6 is in an abnormal operation. , Flag F is set to "1".

On the other hand, if the output of the fully closed switch 6 is ON indicating the fully closed state in step 502, it is determined that the fully closed switch 6 is normal, the counter CFiDL is cleared to "0" in step 510, and the step 511 is performed. The flag F is set to "0" indicating the normal operation of the fully closed switch 6. FIG. 6 is an air-fuel ratio calculation routine, which is executed as a part of the main routine or every predetermined time or predetermined crank angle. First step 60
At 0, the intake pressure P _m , the rotation speed Ne, the detected value of the air-fuel ratio of the air-fuel mixture detected by the lean sensor 8 and the like are taken in. In the next step 601, a normal abnormality of the full-closed switch 6 is checked based on the content of the abnormality determination flag F of the full-closed switch 6 for detecting the idling state, and if normal (flag F =
In step 0), the process proceeds to step 602, and it is determined whether the output of the fully closed switch 6 is on, that is, the throttle valve opening θ is θ ₁ (1.5 °) or less. If the output of the fully closed switch 6 is on, it is determined that the engine is in the idle state, and as shown in FIG. 3, the air-fuel ratio characteristic M3 preset with respect to the rotation speed Ne is changed to the rotation speed at that time. A corresponding lean air-fuel ratio is calculated in step 603. On the contrary, if the output of the fully closed switch is off, it is judged that the engine is not in the idle state, and as shown in FIG. 4, from the characteristic M2 of the air-fuel ratio preset with respect to the intake pressure Pm, the intake pressure Pm at that time is calculated. In step 604, the lean air-fuel ratio corresponding to the above is calculated. In step 601, the flag F is "1".
That is, if the fully closed switch 6 is abnormal, the air-fuel ratio corresponding to the intake pressure Pm at that time is calculated in step 605 from the air-fuel ratio characteristic M1 shown in FIG.

That is, as shown in FIG. 3, the air-fuel ratio at idling depends on the rotation speed Ne as shown in FIG. 3 as long as the full-closed switch 6 is normal, and the step 6 is made leaner than the theoretical air-fuel ratio (A / F≈14.8).
Although it is set in 03, step 603 cannot be executed if the fully closed switch 6 is abnormal. Therefore, regardless of the air-fuel ratio characteristic M3 shown in FIG. 3, the air-fuel ratio characteristic M1 shown in FIG. As a result, particularly at the intake pressure Pm <400 mmHg corresponding to the idling state, it is set to approximately the theoretical air-fuel ratio.

When the target air-fuel ratio is set in steps 603 to 605 as described above, the following publicly known control is performed. In brief, in step 606, the fuel injection amount, that is, the fuel injection time is calculated according to the intake pressure Pm, the rotational speed Ne, etc. at that time so that this target air-fuel ratio is achieved. In step 607, the fuel injection time calculated in step 606 is feedback-corrected by the air-fuel ratio of the air-fuel mixture detected by the lean sensor 8. That is, when the air-fuel ratio detected by the lean sensor 8 is richer than the target air-fuel ratio, the fuel injection time is shortened,
In the opposite case, the fuel injection time is extended and the lean sensor 8
Feedback control of the air-fuel ratio using the output of In step 608, the fuel injection time corrected in step 607 is set in the drive circuit 104 to operate the fuel injection valve 13.

In the above embodiment, the fully closed switch 6 and the step
602 corresponds to the throttle valve fully closed detecting means of the present invention, steps 501 to 511 correspond to the abnormality determining means of the present invention, step 600 corresponds to the load detecting means of the present invention, and step 60
1, 605 correspond to the air-fuel ratio changing means of the present invention, and step 60
3 corresponds to the idling air-fuel ratio setting means of the present invention, step 604 corresponds to the lean air-fuel ratio setting means of the present invention, and steps 606 to 608 correspond to the air-fuel ratio control means of the present invention.

In the above embodiment, the air-fuel ratio characteristics M1 and M2 are set according to the intake pressure Pm as shown in FIG. 4 according to the operating state of the engine. However, as shown in FIG. 7 and FIG. it may be set by the intake air amount Q _a or the like, may be set by both the intake pressure Pm and the rotational speed Ne as shown in FIG. 9.

Further, in the above embodiment, the abnormal operation of the fully closed switch 6 for detecting the idling state is judged by the output state of the fully closed switch 6 at the time when the vehicle is stopped from the running state. You may go if it is persistent. In this case, even if the transmission of the vehicle is in the neutral state and the intake pressure, the rotational speed, the fuel injection time, etc. are values corresponding to the time when the throttle valve is fully closed and idling, the output of the fully closed switch 6 causes the throttle valve to open. It suffices to detect that the valve is off.

[Advantages of the Invention] As described above, according to the present invention, when the abnormality of the throttle valve fully-closed detection means is determined, the air-fuel ratio in the low load state corresponding to the idling state automatically becomes close to the theoretical air-fuel ratio. Since the setting is made, there is an excellent effect that it is possible to surely prevent the air-fuel mixture from becoming a lean air-fuel ratio and greatly destabilizing the idle speed even when the throttle valve full-closed detecting means is abnormal.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing a schematic configuration of the present invention, and FIG.
FIG. 3 is an overall configuration diagram showing an overall configuration of an embodiment of the present invention,
Fig. 4 is an air-fuel ratio characteristic diagram showing the air-fuel ratio with respect to the rotational speed during idling, Fig. 4 is an air-fuel ratio characteristic diagram showing the air-fuel ratio with respect to the intake pressure other than during idling, and Fig. 5 is the execution of the control circuit shown in Fig. 2. FIG. 6 is a flow chart showing an abnormality detection routine, FIG. 6 is a flow chart showing an air-fuel ratio calculation routine executed by the control circuit shown in FIG. 2, and FIGS. 7 to 9 are other examples of the air-fuel ratio characteristic shown in FIG. FIG. 4 is an air-fuel ratio characteristic diagram showing 1 ... Internal combustion engine, 4 ... Pressure sensor as load detecting means, 6 ... Fully closed switch as idling detecting means, 1
0 ... Control circuit including lean air-fuel ratio setting means, idling air-fuel ratio setting means, mixture control means, abnormality determination means, and air-fuel ratio changing means.

Claims (2)

(57) [Claims] 1. Load detecting means for detecting an engine load state based on at least one operating state of an intake pipe pressure, a rotational speed, and an intake air amount of the internal combustion engine; and a throttle valve fully closed as an idling state of the internal combustion engine. Throttle valve fully closed detection means for detecting the state, and the air-fuel ratio is set according to the load state detected by the load detection means so that the air-fuel ratio becomes leaner than the theoretical air-fuel ratio in the low load state including the idling state. A lean air-fuel ratio setting means, an idling air-fuel ratio setting means for setting an air-fuel ratio in an idling state to a substantially theoretical air-fuel ratio, and a fully closed state of the throttle valve is not detected by the throttle valve fully closed detection means. With the air-fuel ratio set by the lean air-fuel ratio setting means, the throttle valve fully-closed detection means fully closes the throttle valve. Is detected, the air-fuel ratio control means for controlling the air-fuel ratio of the internal combustion engine at the air-fuel ratio set by the idling air-fuel ratio setting means, and the abnormality determination for determining the abnormal operation of the throttle valve fully closed detection means And a means for determining the abnormality of the throttle valve fully closed detecting means, the lean air-fuel ratio in the low load state corresponding to the idling state set by the lean air-fuel ratio detecting means is set to approximately the theoretical air-fuel ratio. An air-fuel ratio control device for an internal combustion engine, comprising: 2. The abnormality determining means, when the throttle valve fully closed detecting means does not detect the fully closed state of the throttle valve when the vehicle shifts from a running state to a stopped state,
The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein it is determined that the throttle valve fully closed detection means is abnormal.